Past work in our laboratory established the x-ray dose-response characteristics of the rat parotid gland over the dose range of 0.4-6.kR. These base-line studies utilized both morphologic and physiologic criteria; electron microscopy established the morphologic response and size and residual amylase content the physiologic condition of the gland following irradiation. Our current work is involved with attempting to protect the parotid from the ravages of high doses of x-ray utilizing a new experimental chemoradioprotector WR-2721 (S-2 (3-aminopropylamino) ethyl phosphorothioic acid). To date the compound has shown itself to be highly effective in protecting the parotid against loss of size and function during the first week after irradiation. We are attempting to show that the drug will be effective long after irradiation and hope to elucidate the mechanism of the protection. We also anticipate studies which will combine the selective protective effects of WR-2721 on normal tissues with the equally selective sensitizing effects on tumors of compounds such as metronidazole in an attempt to increase the therapeutic ratio for radiotherapy patients who frequently suffer xerostomia (dry mouth).